Imaging device, imaging system, and manufacturing method of imaging device

ABSTRACT

The imaging device includes a first pixel group and a second pixel group that include a plurality of pixels each having a plurality of photoelectric conversion portions that are separated by an isolation portion and arranged in a first direction and a plurality of transfer gates that transfer charges of the plurality of photoelectric conversion portions. A position of at least a part of the isolation portion within each of the pixels of the first pixel group and a position of at least a part of the isolation portion within each of the pixels of the second pixel group are shifted relative to each other in the first direction. Respective widths of portions where the plurality of separated photoelectric conversion portions overlap with the plurality of transfer gates in a planar view are the same.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to an imaging device, an imaging system,and a manufacturing method of the imaging device.

Description of the Related Art

In CMOS solid state imaging devices, a pupil division phase differencescheme has been proposed as one of the schemes for detecting a focus.Japanese Patent Application Laid-open No. 2012-235444 discloses aconfiguration that shifts the position dividing photoelectric conversionportions of the first pixel and the second pixel of an image capturingpixel group or selects the number of divisions in an x-direction and thenumber of divisions in a y-direction to be co-prime. This configurationis intended to suppress an influence of a low sensitive band occurringdue to the division of photoelectric conversion portions.

In order to perform accurate focus detection in an imaging device of thepupil division phase difference scheme, it is necessary to divide anincident light from imaging optics into pupils in a symmetrical mannerand guide the divided lights to paired photoelectric conversionportions. When pixels having equally divided photoelectric conversionportions only are provided, however, it will be difficult to guide anincident light to the paired photoelectric conversion portions in asymmetrical manner when the incident light is a high incident-anglelight to a short pupil distance lens, in particular, in a peripheralimage height.

As one of the solutions to this problem, it appears to be effective toshift the dividing position of the photoelectric conversion portions.However, a shift of the dividing position of the photoelectricconversion portions causes a difference of charge transfercharacteristics or degradation of charge transfer characteristics of thepaired photoelectric conversion portions and thus results in a reductionin the focus detection accuracy. Further, when the pupil division pixelfor focus detection also serves as an image capturing pixel, this maycause a problem of a reduction in image capturing characteristics.Although Japanese Patent Application Laid-open No. 2012-235444 disclosesphotoelectric conversion portions divided into unequal parts byisolation portions, there is no reference to the above problems.

The present invention has been made in view of the above problems andintends to improve a focus detection accuracy without causingdegradation of image capturing characteristics in an imaging device witha pupil division phase difference scheme.

SUMMARY OF THE INVENTION

An imaging device in one embodiment of the present invention includes: aplurality of pixels each having a first photoelectric conversion portionand a second photoelectric conversion portion arranged adjacent along afirst direction; an isolation portion arranged between the firstphotoelectric conversion portion and the second photoelectric conversionportion; a first transfer gate that transfers charges of the firstphotoelectric conversion portion; and a second transfer gate thattransfers charges of the second photoelectric conversion portion,wherein, the first photoelectric conversion portion has a first portionand a second portion, the second portion is located at a greaterdistance from the first transfer gate in a second direction than thefirst portion is, and the second direction is different from the firstdirection, the second photoelectric conversion portion has a thirdportion arranged in the same position as the first portion in the seconddirection and a fourth portion arranged in the same position as thesecond portion in the second direction, a width in the first directionof the first portion defined by the isolation portion is greater than awidth in the first direction of the second portion defined by theisolation portion, a width in the first direction of the second portiondefined by the isolation portion is less than a width in the firstdirection of the fourth portion defined by the isolation portion, and aposition of the isolation portion between the first portion and thethird portion is different from a position of the isolation portionbetween the second portion and the fourth portion in the firstdirection.

An imaging device in another embodiment of the present inventionincludes: a plurality of pixels each having a first photoelectricconversion portion and a second photoelectric conversion portionseparated from each other by an isolation portion and arranged adjacentalong a first direction, a first transfer gate that transfers charges ofthe first photoelectric conversion portion, and a second transfer gatethat transfers charges of the second photoelectric conversion portion,in which, a difference between a width in a direction crossing a chargetransfer direction of a portion where the first photoelectric conversionportion overlaps with the first transfer gate in a planar view and awidth in a direction crossing a charge transfer direction of a portionwhere the second photoelectric conversion portion overlaps with thesecond transfer gate in a planar view is smaller than a differencebetween a length of the first photoelectric conversion portion and alength of the second photoelectric conversion portion on a linetraversing the isolation portion in the first direction.

A manufacturing method of an imaging device in another embodiment of thepresent invention is a manufacturing method of an imaging deviceincluding a first pixel group and a second pixel group each including aplurality of pixels, each of the pixels having a plurality ofphotoelectric conversion portions and a plurality of transfer gates thattransfer charges of the plurality of photoelectric conversion portions,the manufacturing method comprising steps of: forming the plurality oftransfer gates on a semiconductor substrate; forming a resist patternsuch that the photoelectric conversion portions are separated intomultiple parts in a first direction by an isolation portion, wherein (i)a position of at least a part of the isolation portion in each of thepixels of the first pixel group and a position of at least a part of theisolation portion in each of the pixels of the second pixel group areshifted from each other in the first direction, (ii) respective widthsof portions where the plurality of photoelectric conversion portionsoverlap with the plurality of transfer gates in a planar view are thesame, and (iii) the isolation portion includes a first isolation sectionand a second isolation section, the second isolation section is locatedcloser to a transfer gate than the first isolation section is, and thesecond isolation section equally separates the photoelectric conversionportions; and after forming the transfer gate and the resist pattern,implanting ions from an implantation direction having a non-zero-degreetilt angle relative to a normal direction of the semiconductorsubstrate, in which a length of the first isolation section is greaterthan h×tan θ×cos α, where the tilt angle is denoted as θ, an angle of aprojecting direction of the implantation direction on a surface of thesemiconductor substrate relative to a gate length direction of thetransfer gate is denoted as α, and a film thickness of the resistpattern at the step of implanting ions is denoted as h.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an imaging system of a first embodiment.

FIG. 2 is a block diagram of an imaging device of the first embodiment.

FIG. 3 is a schematic diagram of a pixel arrangement of a pixel unit ofthe first embodiment.

FIG. 4A, FIG. 4B and FIG. 4C are schematic diagrams of pupil divisionpatterns of the first embodiment.

FIG. 5A, FIG. 5B and FIG. 5C are diagrams illustrating focus detectionusing a pupil division phase difference scheme of the first embodiment.

FIG. 6A, FIG. 6B and FIG. 6C are schematic diagrams of a pupil divisionpattern of a second embodiment.

FIG. 7 is a schematic diagram of a pixel arrangement of a pixel unit ofa third embodiment.

FIG. 8A, FIG. 8B, FIG. 8C, FIG. 8D and FIG. 8E are schematic diagrams ofa pupil division pattern of the third embodiment.

FIG. 9A, FIG. 9B, FIG. 9C and FIG. 9D are diagrams illustrating amanufacturing method of the imaging device of the first embodiment.

FIG. 10A, FIG. 10B, FIG. 10C and FIG. 10D are diagrams illustrating themanufacturing method of the imaging device of the first embodiment.

FIG. 11 is a diagram illustrating an ion implantation process in forminga photoelectric conversion portion of the first embodiment.

DESCRIPTION OF THE EMBODIMENTS

Preferred embodiments of the present invention will now be described indetail in accordance with the accompanying drawings.

First Embodiment

FIG. 1 is a block diagram of an imaging system 100 having an imagingdevice 1 of the first embodiment. The imaging system 100 may be any typeof apparatus such as a still camera, a video camera, a smartphone, atablet computer, or the like as long as it has an image capturingfunction. As illustrated in FIG. 1, imaging optics include a first lensset 101, a diaphragm 102, a second lens set 103, a third lens set 104,and an optical low-pass filter 105. The first lens set 101 is arrangedat the front end of the imaging optics and held in a retractable mannerin an optical axis direction. The diaphragm 102 performs light amountadjustment by adjusting an aperture thereof when a capturing isperformed. The second lens set 103 implements a variable magnificationeffect (a zoom function) working together with expansion and retractionof the first lens set 101. The third lens set 104 performs focusadjustment by back-and-forth movement in the optical axis direction.

The optical low-pass filter 105 is an optical element for reducing falsecolor or moire of a captured image. The imaging device 1photoelectrically converts (captures) an object image formed by the lenssets 101, 103, and 104 to generate an image signal (pixel signal). Inthis example, the imaging device 1 is a solid state imaging device suchas a CMOS image sensor with a pupil division phase difference scheme.

An analog image signal output from the imaging device 1 is convertedinto a digital signal (image data) by an analog front end (AFE) 107. Adigital front end (DFE) 108 applies a predetermined calculation processto image data. A digital signal processor (DSP) 109 is a signalprocessor that performs a correction process, a development process, andthe like on image data input from the DFE 108. Further, the DSP 109performs autofocus (AF) calculation that calculates a focus displacementfrom image data.

Image data is recorded in a recording medium 110. A display unit 111 isused for displaying a captured image, various menu windows, or the like,and a liquid crystal display (LCD) or the like is used. A RAM 112temporarily stores image data or the like and is connected to the DSP109. A timing generator (TG) 113 supplies a drive signal to the imagingdevice 1.

A CPU (a controller, a control unit) 114 controls the AFE 107, the DFE108, the DSP 109, the TG 113, a diaphragm drive circuit 115, and ashutter drive circuit 121. Further, the CPU 114 controls a focus drivecircuit 116 based on an AF calculation result of the DSP 109. Anoperation program of the CPU 114 is stored in a ROM 119 or a memory (notdepicted).

The diaphragm drive circuit 115 drives the diaphragm 102 by driving andcontrolling a diaphragm actuator 117. The focus drive circuit 116 causesthe third lens set 104 to move back and forth in the optical axisdirection by driving and controlling a focus actuator 118 and therebyperforms focus adjustment. The ROM 119 stores various correction data orthe like. The mechanical shutter 120 controls the amount of exposure tothe imaging device 1 in a static image capturing. A mechanical shutter120 holds an opening state during a live view operation and a motionimage capturing to keep a state of exposure to the imaging device 1. Theshutter drive circuit 121 controls the mechanical shutter 120.

FIG. 2 is a block diagram of the imaging device 1 of the presentembodiment. The imaging device 1 has a pixel unit 2, a vertical scanningcircuit (VSR) 3, column amplification circuits 4, an output amplifier 5,and a horizontal scanning circuit (HSR) 6. The pixel unit 2 has aplurality of pixels aligned in a two-dimensional matrix in a rowdirection and a column direction. Note that, in the presentspecification, the row direction refers to the horizontal direction inthe drawings, and the column direction refers to the vertical directionin the drawings. Although FIG. 2 depicts pixels of three rows by threecolumns for simplified illustration, the number of pixels is not limitedthereto. Note that a part of pixels may be an optical black (OB) pixelto be shielded.

Each pixel 20 has first and second photoelectric conversion portions 201a and 201 b, first and second transfer transistors M1 a and M1 b, afloating diffusion region 205, a reset transistor M2, an amplificationtransistor M3, and a selection transistor M4. Each of the firstphotoelectric conversion portion 201 a and the second photoelectricconversion portion 201 b is formed of a photodiode. The followingdescription illustrates an example in which transistors of the pixel 20are N-channel MOS transistors. A micro lens is provided over thephotoelectric conversion portions 201 a and 201 b, and a lightconcentrated by the micro lens enters the photoelectric conversionportions 201 a and 201 b. In such a way, two photoelectric conversionportions 201 a and 201 b form a photoelectric conversion unit 201 havingdivided pupils. Note that the number of photoelectric conversionportions forming the photoelectric conversion unit 201 is not limited totwo and may be two or more.

The transfer transistors M1 a and M1 b are provided associated with thephotoelectric conversion portions 201 a and 201 b and drive pulses PTXAand PTXB are applied to respective gates thereof. In response to thedrive pulses PTXA and PTXB being high level, the transfer transistors M1a and M1 b are turned on (in a conductive state), and signals of thephotoelectric conversion portions 201 a and 201 b are transferred to thefloating diffusion region 205 that is an input node of the amplificationtransistor M3. Then, in response to the drive pulses PTXA and PTXB beinglow level, the transfer transistors M1 a and M1 b are turned off (in anon-conductive state). By turning on or off the transfer transistors M1a and M1 b, charges of the photoelectric conversion portions 201 a and201 b can be independently transferred to the floating diffusion region205. The amplification transistor M3 outputs, to a column signal line41, a signal based on charges transferred to the floating diffusionregion 205.

The source of the reset transistor M2 is connected to the floatingdiffusion region 205, and a drive pulse PRES is applied to the gatethereof. In response to the drive pulse PRES being high level, the resettransistor M2 is turned on and a reset voltage is supplied to thefloating diffusion region 205. The selection transistor M4 is providedbetween the amplification transistor M3 and the column signal line 41,and a drive pulse PSEL is applied to the gate of the selectiontransistor M4. In response to the drive pulse PSEL being high level, theamplification transistor M3 and the column signal line 41 areelectrically conducted.

The column signal lines 41 are provided on a column basis, and currentsources 42 are electrically connected to respective column signal lines41. Each current source 42 supplies a bias current to the source of eachamplification transistor M3 via each column signal line 41, and theamplification transistor M3 operates as a source follower.

The vertical scanning circuit 3 supplies drive pulses to respectivegates of the transfer transistors M1 a and M1 b, the reset transistorM2, and the selection transistor M4 on each row. The drive pulses aresupplied on a row basis, sequentially or at random. The verticalscanning circuit 3 is able to perform a readout mode which causes eitherone of the transfer transistors M1 a and M1 b to be in a conductivestate and another readout mode which causes both of the transfertransistors M1 a and M1 b to be in a conductive state.

The column amplification circuits 4 as readout circuits are provided ona column basis and connected to column signal lines 41 directly or viaswitches. Each column amplification circuit 4 has an operationalamplifier 400, a reference voltage source 402, an input capacitor CO, afeedback capacitor Cf, holding capacitors CTS1, CTS2, CTN1, and CTN2,and switches 401 and 403 to 410.

A first node of the input capacitor CO is electrically connected to thecolumn signal line 41, and a second node is electrically connected tothe inverting input node of the operational amplifier 400. A first nodeof the feedback capacitor Cf is electrically connected to the invertinginput node of the operational amplifier 400 and the second node of theinput capacitor CO. A second node of the feedback capacitor Cf iselectrically connected to the output node of the operational amplifier400.

The switch 401 is provided in parallel to the feedback capacitor Cf andcontrols electrical connection of a feedback path between the invertinginput node and the output node of the operational amplifier 400. Whenthe switch 401 is turned off, the operational amplifier 400 performsinverting amplification of a signal on the column signal line 41 at again defined by a ratio of the capacitance of the input capacitor CO andthe capacitance of the feedback capacitor Cf. When the switch 401 isturned on, the operational amplifier 400 operates as a voltage follower.The reference voltage source 402 supplies the reference voltage Vref tothe non-inverting input node of the operational amplifier 400. Theinverting input node and the non-inverting input node of the operationalamplifier 400 are virtually short-circuited and thereby the voltage ofthe inverting input node also becomes the reference voltage Vref.

An output of the operational amplifier 400 is output to the holdingcapacitors CTS1, CTS2, CTN1, and CTN2 via the switches 403 to 406,respectively. The holding capacitors CTS1, CTS2, CTN1, and CTN2 arecapacitors that hold an output from the operational amplifier 400. Abrightness signal at photoelectric conversion of the photoelectricconversion portion 201 a is held in the holding capacitor CTS1 andbrightness signals at photoelectric conversion of the photoelectricconversion portions 201 a and 201 b are held in the holding capacitorCTS2. A signal at resetting is held in the holding capacitors CTN1 andCTN2. The switches 403 to 406 are provided on electrical lines betweenthe holding capacitors CTS1, CTS2, CTN1, and CTN2 and the operationalamplifier 400, respectively, and controls electrical conduction betweenthe output node of the operational amplifier 400 and the holdingcapacitors CTS1, CTS2, CTN1, and CTN2. The switch 403 is controlled by adrive pulse PTSA, and the switch 405 is controlled by a drive pulsePTSAB. Further, the switches 404 and 406 are controlled by a drive pulsePTN.

The switches 407 to 410 are turned on based on signals from thehorizontal scanning circuit 6 and output respective signals held in theholding capacitors CTS1, CTS2, CTN1, and CTN2 to horizontal output lines501 and 502. Brightness signals held in the holding capacitors CTS1 andCTS2 are output to the horizontal output line 501, and reset signalsheld in the holding capacitors CTN1 and CTN2 are output to thehorizontal output lines 502. The output amplifier 5 includes adifferential amplifier and outputs a difference of signals on thehorizontal output lines 501 and 502 to the outside. That is, a signal inwhich a noise component has been removed from a brightness signal byusing correlated double sampling (CDS) is output from the outputamplifier 5. Note that CDS may be performed outside the imaging devicewithout being performed in the output amplifier 5. The horizontalscanning circuit 6 has a shift resistor and outputs signals from thecolumn amplification circuit 4 to the horizontal output lines 501 and502 by sequentially supplying drive pulses to the column amplificationcircuit 4. The configuration described above allows for obtaining an(A+B) signal, which is an addition of the respective signals of thephotoelectric conversion portions 201 a and 201 b, and an A signal ofthe photoelectric conversion portion 201 a. The (A+B) signal is used asan image signal. A B signal of the photoelectric conversion portion 201b can be calculated by subtracting the A signal from the (A+B) signal.Note that the B signal may be separately read out from the photoelectricconversion portion 201 b without performing subtraction. The A signaland the B signal are used as a focus detection signal for phasedifference detection.

FIG. 3 is a schematic diagram of a pixel arrangement of the pixel unit 2of the present embodiment and depicts pixels 20 of six columns by sixrows. Multiple sets of the pixel arrangement of six columns by six rowsillustrated in FIG. 3 are repeatedly arranged on a surface, allowing foracquisition of a high resolution image. Color filters are arranged in apixel unit 2 according to the Bayer arrangement and, on the pixels 20 onodd-numbered rows, color filters of R (red) and G (green) are arrangedin this order from the left in an alternating manner. Further, on thepixels 20 on even-numbered rows, color filters of G and B (blue) arearranged in this order from the left in an alternating manner. Notethat, the advantage of the present invention can be obtained in a caseof a monochrome imaging device, and thus color filters are notnecessarily required. Further, complementary colors such as cyan,magenta, yellow, and the like may be used.

Each of the pixels 20 has a plurality of photoelectric conversionportions 201 a and 201 b, which are separated from each other byisolation portions, and a micro lens 207. The photoelectric conversionportion 201 a and the photoelectric conversion portion 201 b share asingle micro lens 207. In the present embodiment, the photoelectricconversion portion 201 a and the photoelectric conversion portion 201 bof each of all the pixels 20 are divided into two in the horizontaldirection as a first direction (+x-direction or −x-direction) andaligned in the horizontal direction. Output signals of the divided(separated) photoelectric conversion portions 201 a and 201 b can beread out independently. The pixel unit 2 comprises a first pixel group,a second pixel group, and a third pixel group that are different in thepupil division pattern. A position of at least a part of an isolationportion in each pixel of any one of the first to third pixel groups isshifted in the dividing direction (the first direction) relative to aposition of at least a part of an isolation portion in each pixel of theremaining pixel groups. Note that, in the following description, whilethe horizontal direction (+x-direction or −x-direction) is defined asthe dividing direction (the first direction), the vertical direction(+y-direction or −y-direction) may be defined as the dividing direction.

In each pixel 20A of the first pixel group, the dividing positionbetween the photoelectric conversion portion 201 a (R1 a, G1 a, B1 a)and the photoelectric conversion portion 201 b (R1 b, G1 b, B1 b) isshifted in the −x-direction relative to the dividing positions in thepixels 20B and 20C of the second and third pixel groups. Further, ineach pixel 20B of the second pixel group, each dividing position betweenthe photoelectric conversion portion 201 a (R2 a, G2 a, B2 a) and thephotoelectric conversion portion 201 b (R2 b, G2 b, B2 b) is shifted inthe +x-direction relative to the dividing positions in the first andthird pixel groups. In each pixel 20C of the third pixel group, eachdividing position between the photoelectric conversion portion 201 a (R3a, G3 a, B3 a) and the photoelectric conversion portion 201 b (R3 b, G3b, B3 b) is on the pixel center line.

FIG. 4A to FIG. 4C are schematic diagrams of pupil division patterns ofa pixel of the first embodiment and illustrates a part of the pixel in aplanar view. FIG. 4A illustrates a pupil division pattern of the pixel20A of the first pixel group. In the pixel 20A of the first pixel group,the photoelectric conversion portions 201 a (R1 a, G1 a, B1 a) and 201 b(R1 b, G1 b, B1 b) are divided from each other by an isolation portion202A and aligned in the x-direction (the first direction). The isolationportion 202A comprises first to third isolation sections 202Aa to 202Ac.The first isolation section 202Aa is shifted by a distance d in thehorizontal direction (−x-direction) with respect to the pixel centerline C. That is, the difference between the length of the firstphotoelectric conversion portion 201 a and the length of the secondphotoelectric conversion section 201 b on a line traversing the firstisolation section 202Aa in the first direction is the distance d. Thesecond isolation section 202Ab is located on the pixel center line C,and the third isolation section 202Ac connects the first isolationsection 202Aa to the second isolation section 202Ab. The secondisolation section 202Ab is located closer to transfer gate polysilicon204 a and 204 b than the isolation sections 202Aa and 202Ac are. Thesecond isolation section 202Ab is located on the pixel center line C andequally divides the photoelectric conversion portions 201 a and 201 b.Here, the pixel center line C is a virtual line that equally divides thephotoelectric conversion unit 201 in the horizontal direction. Thephotoelectric conversion portions 201 a and 201 b are divided in anasymmetrical manner with respect to the pixel center line C, and thearea of the photoelectric conversion portion 201 b is larger than thearea of the photoelectric conversion portion 201 a.

The configuration described above may be paraphrased by the followingillustration. The photoelectric conversion portion 201 a has a firstportion and a second portion that is at greater distance from thetransfer gate 204 a in the second direction (the y-direction) than thefirst portion is. The photoelectric conversion portion 201 b has, in thefirst direction, a third portion arranged in the same position as thefirst portion and a fourth portion arranged in the same position as thesecond portion. That is, the first portion and the third portion areportions divided equally in the first direction by the isolation section202Ab, and the second and fourth portions are portions divided in anasymmetrical manner by the isolation section 202Aa. In the firstdirection, a width D1 of the first portion defined by the isolationportion 202A is greater than or equal to a width D3 of the third portiondefined by the isolation portion 202A. Further, a width D2 of the secondportion defined by the isolation portion 202A is less than a width D4 ofthe fourth portion defined by the isolation portion 202A. The positionof the isolation portion 202A between the first portion and the thirdportion is different from the position of the isolation portion 202Abetween the second portion and the fourth portion in the firstdirection. That is, the first isolation section 202Aa is shifted by thedistance d in the first direction (the −x-direction) relative to thethird isolation section 202Ac.

The transfer gate polysilicon 204 a and 204 b function as respectivegates of the transfer transistors M1 a and M1 b. The photoelectricconversion portion 201 a and the floating diffusion region 205 a sharethe source/drain regions of the transfer transistor M1 a. Applying avoltage to the transfer gate polysilicon 204 a causes charges to betransferred from the photoelectric conversion portion 201 a to thefloating diffusion region 205 a. Similarly, the photoelectric conversionportion 201 b and the floating diffusion region 205 b share thesource/drain regions of the transfer transistor M1 b. Applying a voltageto the transfer gate polysilicon 204 b causes charges to be transferredfrom the photoelectric conversion portion 201 b to the floatingdiffusion region 205 b.

A part of each of the transfer gate polysilicon 204 a and 204 b overlapswith each of the photoelectric conversion portions 201 a and 201 b in aplanar view. Respective width directions of the transfer gatepolysilicon 204 a and 204 b are the same. A width W1 of a portion wherethe first photoelectric conversion portion 201 a overlaps with the firsttransfer gate polysilicon 204 a is equal to a width W2 of a portionwhere the second photoelectric conversion portion 201 b overlaps withthe second transfer gate polysilicon 204 b. This allows forsubstantially the same charge transfer characteristics between thetransfer transistors M1 a and M1 b. That is, it is possible to maintainthe symmetry of charge transfer characteristics while dividing thephotoelectric conversion portions 201 a and 201 b in an asymmetricalmanner.

FIG. 4B illustrates a pupil division pattern of the pixel 20B of thesecond pixel group. The photoelectric conversion portions 201 a (R2 a,G2 a, B2 a) and 201 b (R2 b, G2 b, B2 b) are divided by an isolationportion 202B. The isolation portion 202B comprises isolation sections202Ba to 202Bc. Unlike the case of FIG. 4A, the first isolation section202Ba is located decentered by the distance d in the +x-direction withrespect to the pixel center line C. The second isolation section 202Bbis located on the pixel center line C, and the third isolation section202Bc connects the first isolation section 202Ba to the second isolationsection 202Bb. Also in FIG. 4B, the width W1 of the overlapping portionis equal to the width W2 of the overlapping portion. Further, therelationships among the first to fourth portions described in detailwith respect to FIG. 4A can similarly apply to the case of FIG. 4B withinterpretation of the photoelectric conversion portions 201 a and 201 bbeing replaced with each other.

FIG. 4C illustrates a pupil division pattern of the pixel 20C of thethird pixel group. The photoelectric conversion portions 201 a (R3 a, G3a, B3 a) and 201 b (R3 b, G3 b, B3 b) are divided at the center of thepixel by an isolation portion 202C in the horizontal direction. Theisolation portion 202C has a straight shape and is located on the pixelcenter line C. Also in FIG. 4C, the width W1 of the overlapping portionis equal to the width W2 of the overlapping portion.

In FIG. 4A to FIG. 4C, focus detection is enabled by separately readingout signals that are based on charges of the photoelectric conversionportions 201 a and 201 b. On the other hand, formation of a signal of anormal captured image is enabled by combining signals that are based oncharges of the photoelectric conversion portions 201 a and 201 b.

FIG. 5A to FIG. 5C are diagrams illustrating focus detection using apupil division phase difference scheme. FIG. 5A illustrates a schematicsectional view of the pixel 20 in the present embodiment. The pixel 20forms a solid state imaging device of a pupil division phase differencescheme, and a single micro lens 207 is formed over (in the +z-direction)of the paired photoelectric conversion portions 201 a and 201 b. Theimaging optics (101 to 105) of FIG. 1 are further provided above themicro lens 207. A light flux R from the imaging optics is guided to alight receiving surface 206 via the micro lens 207.

FIG. 5B and FIG. 5C are diagrams of the light receiving surface 206 whenviewed from the imaging optics (from the +z-direction). The light flux Ris concentrated by the micro lens 207 and projected as an exit pupilimage R1 on the light receiving surface 206. In order to performaccurate focus detection in a solid state imaging device of a pupildivision phase difference scheme, it is necessary to divide an incidentlight flux from imaging optics into pupils in a symmetrical manner andguide the divided light fluxes to the paired photoelectric conversionportions 201 a and 201 b. FIG. 5B illustrates the pixel 20 located atsubstantially the center of an image capturing region. In this pixel 20,the exit pupil image R1 is divided substantially equally and projectedon the paired photoelectric conversion portions 201 a and 201 b. In thiscase, respective charges generated in the photoelectric conversionportions 201 a and 201 b are substantially equal. FIG. 5C illustratesthe pixel 20 located at the end of the image capturing region. In thispixel, the exit pupil image R1 is divided and projected on the pairedphotoelectric conversion portions 201 a and 201 b in an asymmetricalmanner, and therefore a difference occurs between respective chargesgenerated in the photoelectric conversion portions 201 a and 201 b. Thatis, signals read out from the pixels 20 are different depending on theposition of the pixel 20 in the image capturing region, and this resultsin a reduction in the focus detection accuracy. In particular, when ahigh incident-angle light enters a short pupil distance lens, a poorsymmetry of the exit pupil image R1 in the pixels 20 located at the endof the capturing region makes it difficult to perform focus detection.

To address this problem, the imaging device of the present embodimenthas the first to third pixel groups that are different in the dividingposition of the photoelectric conversion portions 201 a and 201 b. Inthe pixel 20A of the first pixel group, the photoelectric conversionportions 201 a and 201 b are divided by the isolation portion 202Adecentered in the −x-direction from the pixel center. Further, in thepixel 20B of the second pixel group, the photoelectric conversionportions 201 a and 201 b are divided by the isolation portion 202Bdecentered in the +x-direction from the pixel center line C. Further, inthe pixel 20C of the third pixel group, the photoelectric conversionportions 201 a and 201 b are divided by the isolation portion 202C atthe pixel center. According to the present embodiment, a reduction inthe focus detection accuracy can be suppressed by properly selectingpixel signals of the first to third pixel groups in accordance with thedecentering position of the exit pupil image R1.

For example, when the exit pupil image R1 is shifted in the +x-directionas illustrated in FIG. 5C, focus detection is performed by using thesignal from the pixel 20B of the second pixel group. The photoelectricconversion portions 201 a and 201 b of the pixel 20B are divided at theposition decentered in the +x-direction. Since the exit pupil image R1is projected on the photoelectric conversion portions 201 a and 201 b ina symmetrical manner, a use of the signal of the pixel 20B of the secondpixel group for focus detection allows for maintaining the focusdetection accuracy.

On the other hand, when the exit pupil image R1 is shifted in the−x-direction, focus detection is performed by using the signal from thepixel 20A of the first pixel group. Since the photoelectric conversionportions 201 a and 201 b of the pixel 20A are divided at the positiondecentered in the −x-direction, the exit pupil image R1 is projected onthe photoelectric conversion portions 201 a and 201 b in a symmetricalmanner. Therefore, also in this case, the focus detection accuracy canbe maintained. Note that selection of the first to third pixel groupsmay be performed by the CPU 114 and/or the DSP 109 illustrated in FIG.1.

Moreover, in the present embodiment, the pixels 20A to 20C of the firstto third pixel groups have the same widths W1 and W2 of the portionswhere the photoelectric conversion portions 201 a and 201 b overlap withthe transfer gate polysilicon 204 a and 204 b, respectively. That is,the width W1 in the direction crossing a charge transfer direction of aportion where the photoelectric conversion portion 201 a overlaps withthe transfer gate polysilicon 204 a is equal to the width W2 in thedirection crossing a charge transfer direction of a portion where thephotoelectric conversion portion 201 b overlaps with the transfer gatepolysilicon 204 b. This can suppress the charge transfer characteristicsfrom being asymmetrical, even when the dividing position between thephotoelectric conversion portions 201 a and 201 b is decentered. Thisallows for obtaining substantially the same capturing characteristics asthose of a solid state imaging device with a pupil division phasedifference scheme comprising only pixels each of which has the equallydivided photoelectric conversion portions. Note that the widths W1 andW2 may not necessarily be the same and, as long as the differencebetween the widths W1 and W2 is smaller than the difference (thedistance d) between the length of the first photoelectric conversionportion 201 a in the x-direction and the length of the secondphotoelectric conversion portion 201 b in the x-direction, a decrease inthe symmetry of the charge transfer characteristics can be reduced.

Next, a manufacturing method of the imaging device of the presentembodiment will be described by using FIG. 9A to FIG. 11. FIG. 9A toFIG. 9D each illustrate a cross section along the line I-I′ of FIG. 4A,and FIG. 10A to FIG. 10D each illustrate a cross section along the lineII-II′ of FIG. 4A. The semiconductor substrate 200 is a siliconsemiconductor substrate, for example, and a P-type semiconductor well200 a, for example, is formed in a capturing region of the semiconductorsubstrate 200. After a device isolation portion is formed in thesemiconductor substrate 200, a gate oxide film 208 and a polysiliconfilm 204′ are deposited. Next, a photoresist is applied, exposed, anddeveloped on the polysilicon film 204′ to form a photoresist pattern 203(FIG. 9A, FIG. 10A).

Next, the polysilicon film 204′ is etched by using the photoresistpattern 203 as a mask and patterned in a similar manner to thephotoresist pattern 203. Thereby, the transfer gate polysilicon 204 a isformed (FIG. 9B, FIG. 10B). Next, a photoresist pattern 209 is formed asan ion implantation mask for forming the photoelectric conversionportions 201 a and 201 b. The photoresist pattern 209 is formed so as tocover a part of the substrate and has openings used for forming thephotoelectric conversion portions 201 a and 201 b. An ion implantationis performed by using the photoresist patterns 203 and 209 as masks toform the photoelectric conversion portions 201 a and 201 b (FIG. 9C,FIG. 10C). As illustrated in FIG. 10C, no ion is implemented under thephotoresist pattern 209 between the openings, and thus the isolationportion 202A dividing the photoelectric conversion portions 201 a and201 b is formed. The photoresist patterns 203 and 209 are then removed(FIG. 9D, FIG. 10D). Furthermore, as illustrated in FIG. 5A, aninsulating film, a shield film, a wiring layer, vias, micro lenses, apassivation layer, and the like are formed to obtain the pixels 20A to20C.

FIG. 11 illustrates an ion implantation process when the photoelectricconversion portions 201 a and 201 b are formed in FIG. 9C and FIG. 10C,and illustrates a cross section along the line I-I′ of FIG. 4A and FIG.4B. In the well 200 a, an accumulation region 2011 of the photoelectricconversion portion 201 a and the drain region (the floating diffusionregion) 205 of the transfer transistor M1 are formed. The accumulationregion 2011 is formed of an N-type semiconductor, and the surfacethereof is covered with a dense P-type semiconductor layer 2012. Acharge transferring region 2013 functions as the source of the transfertransistor M1 that transfers charges of the accumulation region 2011 tothe drain (the floating diffusion region) 205 a. The gate oxide film 208is a silicon oxide film, for example, and is formed so as to cover thephotoelectric conversion portions 201 a and 201 b and the drain (thefloating diffusion region) 205. The transfer gate polysilicon 204 a isformed on the gate oxide film 208, and a part of the transfer gatepolysilicon 204 a overlaps with the charge transferring region 2013 ofthe photoelectric conversion portion 201 a in a planar view.

The photoresist pattern 209 is a mask in an ion implantation process forforming the accumulation region 2011 and the charge transferring region2013 of the photoelectric conversion portion 201 a. As illustrated herein FIG. 11, a normal direction of the semiconductor substrate 200 isdefined as a z-axis, the gate length direction of the transfer gatepolysilicon 204 a is defined as a y-axis, and the gate width directionis defined as an x-axis.

In the present embodiment, the charge transferring region 2013 is formedin a self-aligning manner with respect to the transfer gate polysilicon204 a, and the ion implantation is performed from an implantationdirection 610, which is tilted by a predetermined angle and thus is not0 degree relative to the z-axis. With ion implantation from the tiltedimplantation direction 610, however, no ion is implemented to a region612 behind the photoresist pattern 209.

A length L2 in the y-direction of the region 612 is expressed by h×tanθ×cos α, where an angle (tilt angle) of the implantation direction 610relative to the negative direction of the z-axis is denoted as θ, theangle of a vector 611, which is a projected vector on the xy-plane ofthe implantation direction 610, relative to the positive direction ofthe y-axis is denoted as α, and a film thickness of the photoresistpattern 209 is denoted as h. Therefore, in order to form the chargetransferring region 2013, it is preferable that at least the distancebetween an edge 2041 of the transfer polysilicon 204 and an edge 2091 ofthe photoresist pattern 209 be greater than the length L2 expressed byh×tan θ×cos α. The length L2 corresponds to the length L1 of each of thesecond isolation sections 202Ab and 202Bb, which divides thephotoelectric conversion portions into equal parts, of the isolationportions 202A and 202B of FIG. 4A and FIG. 4B. That is, it is preferablethat the length L1 of each of the second isolation sections 202Ab and202Bb of the isolation portions 202A and 202B be greater than the lengthL2 expressed by h×tan θ×cos α.

The pixels 20A to 20C obtained in such a way has the followingconfiguration. That is, (i) the position of at least a part of theisolation portions in the pixels 20A to 20C of the first to third pixelgroups is shifted in the dividing direction relative to the position ofat least a part of the isolation portion in the pixels of remainingpixel groups. (ii) Respective widths of the portions where a pluralityof photoelectric conversion portions 201 a and 201 b overlap with aplurality of transfer gate polysilicon 204 a and 204 b in a planar vieware the same. (iii) The isolation portions 202A and 202B include thefirst isolation sections 202Aa and 202Ba and the second isolationsections 202Ab and 202Bb, respectively, the second isolation sections202Ab and 202Bb are located closer to the transfer gate polysilicon thanthe first isolation sections 202Aa and 202Ba are, and each of the secondisolation sections 202Ab and 202Bb equally divides the photoelectricconversion portions 201 a and 201 b.

According to the present embodiment, while providing pixel groups havingdifferent dividing positions of the photoelectric conversion portions,it is possible to suppress degradation of charge transfercharacteristics which would otherwise be caused due to thedecentrization of the dividing positions of the photoelectric conversionportions. Further, the manufacturing method of the imaging deviceaccording to the present embodiment allows for optimum design of thelength of respective sections of the isolation portion in accordancewith the angle of ion implantation.

Second Embodiment

An imaging device of the second embodiment will be described mainly forconfigurations different from those of the first embodiment. FIG. 6A toFIG. 6C are schematic diagrams of dividing patterns of a pixel of animage capturing pixel group in the second embodiment and each illustratea part of the pixel in a planar view. FIG. 6A illustrates a pixel 21A ofa first pixel group, FIG. 6B illustrates a pixel 21B of a second pixelgroup, and FIG. 6C illustrates a pixel 21C of a third pixel group. In asimilar manner to the first embodiment, the photoelectric conversionportions 201 a and 201 b are divided in the horizontal direction (thex-direction) by isolation portions 202A, 202B, and 202C. The isolationportion 202A is decentered by the distance d in the −x-direction fromthe pixel center line C, and the isolation portion 202B is decentered bythe distance d in the +x-direction from the pixel center line C.Further, the isolation portion 202C is located on the pixel center lineC.

In the present embodiment, the isolation portions 202A and 202B of thefirst and second pixel groups have a straight shape similarly to theisolation portion 202C of the third pixel group. The transfer gatepolysilicon 204 a and 204 b are arranged with an angle of 45 degreesrelative to the x-direction and the y-direction, respectively, andrespective width directions thereof are orthogonal to each other.Further, the transfer gate polysilicon 204 a and 204 b overlap withrespective corners of the photoelectric conversion portions 201 a and201 b in a planar view. The width W1 of a portion where the firstphotoelectric conversion portion 201 a overlaps with the first transfergate polysilicon 204 a is equal to the width W2 of a portion where thesecond photoelectric conversion portion 201 b overlaps with the secondtransfer gate polysilicon 204 b. This allows for substantially the samecharacteristics of charge transfer of the transfer transistors M1 a anM1 b. That is, while dividing the photoelectric conversion portions 201a and 201 b in an asymmetrical manner, it is possible to maintain thesymmetry of charge transfer characteristics. Note that, with thedifference of widths W1 and W2 being less than the distance d, adecrease in the symmetry of charge transfer characteristics can bereduced.

Also in the present embodiment, a reduction of the focus detectionaccuracy can be suppressed by properly selecting pixel signals of thefirst to third pixel groups in accordance with a decentering state of anexit pupil image. When an exit pupil image is shifted in the+x-direction, the pixel signal of the second pixel group can be used toperform focus detection. Further, when an exit pupil image is shifted inthe −x-direction, the pixel signal of the first pixel group can be usedto perform focus detection. In such a way, a proper selection of thefirst to third pixel groups in accordance with a decentering state of anexit pupil image allows the exit pupil image to be projected on thephotoelectric conversion portions 201 a and 201 b in a symmetricalmanner to maintain the focus detection accuracy.

In the present embodiment, the isolation portion 202A of the first pixelgroup and the isolation portion 202B of the second pixel group each havea straight shape, and each of the entire isolation portions 202A and202B is decentered by the distance d from the pixel center line C. Thelength of a portion decentered from the pixel center line C of theisolation portions 202A and 202B is longer than the length of the firstisolation sections 202Aa and 202Bb in the first embodiment. The dividingposition of the photoelectric conversion portions 201 a and 201 b withrespect to the pixel center line C is constant in the y-direction, whichcan enhance the advantage of maintaining the symmetry of pupil divisionagainst a shift of the exit pupil image in the x-direction.

Third Embodiment

An imaging device of the third embodiment will be described mainly forconfigurations different from those of the first and second embodiments.FIG. 7 is a schematic diagram of a pixel arrangement of the pixel unit 2in the third embodiment and illustrates pixels 22 of five columns byfive rows. Each pixel 22 has first to fourth photoelectric conversionportions 201 a to 201 d quartered by isolation portions and the microlens 207 depicted with a circle, and R, G, and B color filters arearranged to respective pixels 22 according to the Bayer arrangement.Each R pixel 22 has the first photoelectric conversion portion 201 a (R1a to R5 a), the second photoelectric conversion portion 201 b (R1 b toR5 b), a third photoelectric conversion portion 201 c (R1 c to R5 c),and a fourth photoelectric conversion portion 201 d (R1 d to R5 d). EachG pixel 22 has the first photoelectric conversion portion 201 a (G1 a toG5 a), the second photoelectric conversion portion 201 b (G1 b to G5 b),the third photoelectric conversion portion 201 c (G1 c to G5 c), and thefourth photoelectric conversion portion 201 d (G1 d to G5 d). Further,each B pixel 22 has the first photoelectric conversion portion 201 a (B1a to B5 a), the second photoelectric conversion portion 201 b (B1 b toB5 b), the third photoelectric conversion portion 201 c (B1 c to B5 c),and the fourth photoelectric conversion portion 201 d (B1 d to B5 d) (B3a, B3 b, B3 c, and B3 d are not depicted). Note that the advantage ofthe present invention can be obtained in a case of a monochrome imagingdevice, and thus color filters are not necessarily required.

FIG. 8A to FIG. 8E are schematic diagrams of pupil division patterns ofthe pixel of the third embodiment and each illustrate a part of thepixel in a planar view. In the present embodiment, the photoelectricconversion unit 201 of each pixel 22 is divided into four, and a pixelsignal of each of the divided photoelectric conversion portions 201 a to201 d can be read out separately via transfer transistors.

As illustrated in FIG. 8A to FIG. 8E, the pixel unit 2 is formed of fivetypes of pixel groups that are different in the dividing pattern.

FIG. 8A illustrates a pixel 22A of the first pixel group. Thephotoelectric conversion unit 201 is divided into four by a firstisolation portion 202A1 and a second isolation portion 202A2. Theisolation portions 202A1 and 202A2 are orthogonal to each other andintersect at a position shifted in the −x-direction and the +y-directionfrom the pixel center C′ (the center of the photoelectric conversionunit 201). The first isolation portion 202A1 divides the photoelectricconversion unit 201 into two in the x-direction (the first direction),and the second isolation portion 202A2 divides the photoelectricconversion unit 201 into two in the y-direction (the second direction).That is, the photoelectric conversion unit 201 has the firstphotoelectric conversion portion 201 a (R1 a, G1 a, B1 a), the secondphotoelectric conversion portion 201 b (R1 b, G1 b, B1 b), the thirdphotoelectric conversion portion 201 c (R1 c, G1 c, B1 c), and thefourth photoelectric conversion portion 201 d (R1 d, G1 d, B1 d). Thefirst photoelectric conversion portion 201 a has the smallest lightreceiving area in the four photoelectric conversion portions 201 a to201 d, and the fourth photoelectric conversion portion 201 d is thelargest in the four photoelectric conversion portions 201 a to 201 d.Each of the second photoelectric conversion portion 201 b and the thirdphotoelectric conversion portion 201 c is larger than the firstphotoelectric conversion portion 201 a and smaller than the fourthphotoelectric conversion portion 201 d. Further, the secondphotoelectric conversion portion 201 b and the third photoelectricconversion portion 201 c have substantially the same light receivingarea.

The first to fourth transfer gate polysilicon 204 a to 204 d arearranged inclined by an angle of 45 degrees relative to the x-directionand the y-direction and overlap with respective corners of thephotoelectric conversion portions 201 a to 201 d in a planar view. Thefirst transfer polysilicon 204 a and the fourth transfer gatepolysilicon 204 d are arranged in parallel, and the second transfer gatepolysilicon 204 b and the third transfer gate polysilicon 204 c arearranged in parallel. The widths W1 to W4 of portions where the first tofourth photoelectric conversion portions 201 a to 201 d overlap with thefirst to fourth transfer gate polysilicon 204 a to 204 d, respectively,are the same as each other. It is therefore possible to maintain thesymmetry of charge transfer characteristics while dividing thephotoelectric conversion portions 201 a to 201 d in an asymmetricalmanner.

FIG. 8B illustrates a pixel 22B of the second pixel group. A firstisolation portion 202B1 and a second isolation portion 202B2 intersectat a position shifted in the +x-direction and the +y-direction from thepixel center C′ and divide the photoelectric conversion unit 201 intotwo in the x-direction and the y-direction, respectively. The pixel 22Bof the second pixel group has the first photoelectric conversion portion201 a (R2 a, G2 a, B2 a), the second photoelectric conversion portion201 b (R2 b, G2 b, B2 b), the third photoelectric conversion portion 201c (R2 c, G2 c, B2 c), and the fourth photoelectric conversion portion201 d (R2 d, G2 d, B2 d). The second photoelectric conversion portion201 b has the largest light receiving area in the four photoelectricconversion portions, and the third photoelectric conversion portion 201c has the smallest light receiving area in the four photoelectricconversion portions. The first photoelectric conversion portion 201 aand the fourth photoelectric conversion portion 201 d have substantiallythe same light receiving area.

FIG. 8C illustrates a pixel 22C of the third pixel group. A firstisolation portion 202C1 and a second isolation portion 202C2 intersectat a position shifted in the −x-direction and the −y-direction from thepixel center C′ and divide the photoelectric conversion unit 201 intotwo in the x-direction and the y-direction, respectively. The pixel 22Cof the third pixel group has the first photoelectric conversion portion201 a (R3 a, G3 a, B3 a), the second photoelectric conversion portion201 b (R3 b, G3 b, B3 b), the third photoelectric conversion portion 201c (R3 c, G3 c, B3 c), and the fourth photoelectric conversion portion201 d (R3 d, G3 d, B3 d). The third photoelectric conversion portion 201c has the largest light receiving area in the four photoelectricconversion portions, and the second photoelectric conversion portion 201b has the smallest light receiving area in the four photoelectricconversion portions. The first photoelectric conversion portion 201 aand the fourth photoelectric conversion portion 201 d have substantiallythe same light receiving area.

FIG. 8D illustrates a pixel 22D of the fourth pixel group. A firstisolation portion 202D1 and a second isolation portion 202D2 intersectat a position shifted in the +x-direction and the −y-direction from thepixel center C′ and divide the photoelectric conversion unit 201 intotwo in the x-direction and the y-direction, respectively. The pixel 22Dof the fourth pixel group has the first photoelectric conversion portion201 a (R4 a, G4 a, B4 a), the second photoelectric conversion portion201 b (R4 b, G4 b, Bb), the third photoelectric conversion portion 201 c(R4 c, G4 c, B4 c), and the fourth photoelectric conversion portion 201d (R4 d, G4 d, B4 d). The first photoelectric conversion portion 201 ahas the largest light receiving area in the four photoelectricconversion portions, and the fourth photoelectric conversion portion 201d has the smallest light receiving area in the four photoelectricconversion portions. The second photoelectric conversion portion 201 band the third photoelectric conversion portion 201 c have substantiallythe same light receiving area.

FIG. 8E illustrates a pixel 22E of the fifth pixel group. A firstisolation portion 202E1 and a second isolation portion 202E2 intersectat the pixel center C′ and divide the photoelectric conversion unit 201into two in the x-direction and the y-direction, respectively. The pixel22E of the fifth pixel group has the first photoelectric conversionportion 201 a (R5 a, G5 a, B5 a), the second photoelectric conversionportion 201 b (R5 b, G5 b, B5 b), the third photoelectric conversionportion 201 c (R5 c, G5 c, B5 c), and the fourth photoelectricconversion portion 201 d (R5 d, G5 d, B5 d). The first to fourthphotoelectric conversion portions 201 a to 201 d have substantially thesame light receiving area.

In the imaging device illustrated in FIG. 7 and FIG. 8A to FIG. 8E,focus detection can be performed by separately reading out pixel signalsobtained from the first to fourth photoelectric conversion portions 201a to 201 d. On the other hand, a normal captured image can be formed bycombining and reading out pixel signals obtained from the firstphotoelectric conversion portion 201 a (R1 a, G1 a, B1 a), the secondphotoelectric conversion portion 201 b (R1 b, G1 b, B1 b), the thirdphotoelectric conversion portion 201 c (R1 c, G1 c, B1 c), and thefourth photoelectric conversion portion 201 d (R1 d, G1 d, B1 d) in thefirst pixel group. In a similar manner in the second to fifth pixelgroups, a normal captured image can be formed by combining and readingout pixel signals obtained from the first to fourth photoelectricconversion portions 201 a to 201 d.

The photoelectric conversion portions 201 a to 201 d of the first tofourth pixel groups of the imaging device of the present embodiment aredivided by the first isolation portions 202A1 to 202D1 at a positiondecentered in the +x-direction or −x-direction from the pixel center C′.For example, when the exit pupil image R1 is shifted in the +x-directionas illustrated in FIG. 5C, focus detection is performed by using pixelsignals from the second or fourth pixel group. Since the photoelectricconversion units 201 in the pixel 22B of the second pixel group and inthe pixel 22D of the fourth pixel group are divided at the positiondecentered in the +x-direction, the exit pupil image R1 is projected ina symmetrical manner on the photoelectric conversion portions 201 a and201 b and on the photoelectric conversion portions 201 c and 201 d.Thereby, the focus detection accuracy can be maintained. On the otherhand, when the exit pupil image R1 is shifted in the −x-direction, thefocus detection accuracy can be maintained through focus detection byusing pixel signals of the first pixel group or the third pixel groupcomprising pixels in each of which the dividing position of thephotoelectric conversion portions is decentered in the −x-direction.

Further, the photoelectric conversion unit 201 of the imaging device ofthe present embodiment is divided by the second isolation portions 202A2to 202D2 at a position decentered in the +y-direction or the−y-direction from the pixel center C′. For example, when the exit pupilimage R1 is shifted in the +y-direction, the focus detection accuracycan be maintained through focus detection by using pixel signals of thefirst or second pixel group comprising pixels in each of which thedividing position of the photoelectric conversion unit 201 is decenteredin the +y-direction. On the other hand, when the exit pupil image R1 isshifted in the −y-direction, the focus detection accuracy can bemaintained through focus detection by using pixel signals of the thirdor fourth pixel group comprising pixels in each of which the dividingposition of the photoelectric conversion unit 201 is decentered in the−y-direction.

In the present embodiment, the widths W1 to W4 of portions where thephotoelectric conversion portions 201 a to 201 d overlap with thetransfer gate polysilicon 204 a to 204 d, respectively, are the same.This can suppress degradation of charge transfer characteristics whichwould otherwise be caused due to decentering of the dividing positionsof the photoelectric conversion portions 201 a to 201 d. This allows forobtaining substantially the same capturing characteristics as those ofan imaging device with a pupil division phase difference schemecomprising only pixels in each of which the photoelectric conversionunit 201 is divided equally in the x-direction and the y-direction. Inaddition, a decrease in the symmetry of charge transfer characteristicscan be reduced by reducing the difference of the widths W1 to W4compared to the difference between the first isolation portions 202A1 to202D1 and the virtual center and the difference between the secondisolation portions 202A2 to 202D2 and the pixel center C′.

Other Embodiments

Any of the embodiments described above is intended to merely illustratean embodied example of the present invention, and the technical scope ofthe present invention shall not be construed in a limiting sense bythese embodiments. That is, the present invention can be implemented invarious ways without departing from the technical concept or the primaryfeatures thereof. For example, the CMOS transistor may be any of theN-type or P-type. The number of divisions and the direction of divisionof the photoelectric conversion portions are not limited to those in theembodiments described above.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2016-086156, filed Apr. 22, 2016, which is hereby incorporated byreference herein in its entirety.

1.-12. (canceled)
 13. An imaging device comprising: a plurality ofpixels each including a first photoelectric conversion portion, a secondphotoelectric conversion portion, a third photoelectric conversionportion and a fourth photoelectric conversion portion, and a firsttransfer gate that transfers charges of the first photoelectricconversion portion, a second transfer gate that transfers charges of thesecond photoelectric conversion portion, a third transfer gate thattransfers charges of the third photoelectric conversion portion and afourth transfer gate that transfers charges of the fourth photoelectricconversion portion; and a plurality of microlenses each covering thefirst photoelectric conversion portion, the second photoelectricconversion portion, the third photoelectric conversion portion and thefourth photoelectric conversion portion of a corresponding pixel of theplurality of pixels, wherein, the first photoelectric conversion portionand the second photoelectric conversion portion are arranged adjacentalong a first direction, the third photoelectric conversion portion andthe fourth photoelectric conversion portion are arranged adjacent alongthe first direction, the first photoelectric conversion portion and thethird photoelectric conversion portion are arranged adjacent along asecond direction, the third photoelectric conversion portion and thefourth photoelectric conversion portion are arranged adjacent along thefirst direction, and each of the first transfer gate, the secondtransfer gate, the third transfer gate and the fourth transfer gate isarranged so that a channel width direction crosses both the firstdirection and the second direction.
 14. The imaging device according toclaim 13, wherein, each of the plurality of pixels includes a firstisolation section configured to isolate the first photoelectricconversion portion and the second photoelectric conversion portion andto isolate the third photoelectric conversion portion and the fourthphotoelectric conversion portion, a width of the first photoelectricconversion portion in the first direction is different from a width ofthe second photoelectric conversion portion in the first direction, anda width of the third photoelectric conversion portion in the firstdirection is different from a width of the fourth photoelectricconversion portion in the first direction.
 15. The imaging deviceaccording to claim 13, wherein, each of the plurality of pixels includesa second isolation section configured to isolate the first photoelectricconversion portion and the third photoelectric conversion portion and toisolate the second photoelectric conversion portion and the fourthphotoelectric conversion portion, a width of the first photoelectricconversion portion in the second direction is different from a width ofthe third photoelectric conversion portion in the second direction, anda width of the second photoelectric conversion portion in the seconddirection is different from a width of the fourth photoelectricconversion portion in the second direction.
 16. The imaging deviceaccording to claim 13, wherein, each of the plurality of pixels includesa first isolation section configured to isolate the first photoelectricconversion portion and the second photoelectric conversion portion andto isolate the third photoelectric conversion portion and the fourthphotoelectric conversion portion, each of the plurality of pixelsincludes a second isolation section configured to isolate the firstphotoelectric conversion portion and the third photoelectric conversionportion and to isolate the second photoelectric conversion portion andthe fourth photoelectric conversion portion, a width of the firstphotoelectric conversion portion in the first direction is differentfrom a width of the second photoelectric conversion portion in the firstdirection, a width of the third photoelectric conversion portion in thefirst direction is different from a width of the fourth photoelectricconversion portion in the first direction, a width of the firstphotoelectric conversion portion in the second direction is differentfrom a width of the third photoelectric conversion portion in the seconddirection, and a width of the second photoelectric conversion portion inthe second direction is different from a width of the fourthphotoelectric conversion portion in the second direction.
 17. Theimaging device according to claim 14, wherein, the plurality of pixelsincludes a first pixel and a second pixel, in the first pixel, the widthof the first photoelectric conversion portion in the first direction isshorter than the width of the second photoelectric conversion portion inthe first direction, and the width of the third photoelectric conversionportion in the first direction is shorter than the width of the fourthphotoelectric conversion portion in the first direction, and in thesecond pixel, the width of the first photoelectric conversion portion inthe first direction is longer than the width of the second photoelectricconversion portion in the first direction, and the width of the thirdphotoelectric conversion portion in the first direction is longer thanthe width of the fourth photoelectric conversion portion in the firstdirection.
 18. The imaging device according to claim 15, wherein, theplurality of pixels includes a first pixel and a second pixel, in thefirst pixel, the width of the first photoelectric conversion portion inthe second direction is shorter than a width of the third photoelectricconversion portion in the second direction, and the width of the secondphotoelectric conversion portion in the second direction is shorter thana width of the fourth photoelectric conversion portion in the seconddirection, and in the second pixel, the width of the first photoelectricconversion portion in the second direction is longer than a width of thethird photoelectric conversion portion in the second direction, and thewidth of the second photoelectric conversion portion in the seconddirection is longer than a width of the fourth photoelectric conversionportion in the second direction.
 19. The imaging device according toclaim 13, wherein the first transfer gate, the second transfer gate, thethird transfer gate and the fourth transfer gate are located atrespective corners of the first photoelectric conversion portion, thesecond photoelectric conversion portion, the third photoelectricconversion portion and the fourth photoelectric conversion portion. 20.The imaging device according to claim 13, wherein the first transfergate, the second transfer gate, the third transfer gate and the fourthtransfer gate have a same channel width.
 21. An imaging systemcomprising: the imaging device according to claim 13, and a signalprocessing device that processes a signal from the imaging device.